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Home >> Buick >> 2015 >> Regal GS, AWD >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls And Fuel - 2.0L (LTG) - DTC P0010 To DTC P0333 >> Diagnostic Information and Procedures >> DTC P0171 or P0172: Fuel Trim System >> Circuit/System Testing

Circuit/System Testing

  1. Ignition ON.
  2. Verify the manifold absolute pressure sensor is within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure (With LFX)
    • If not within the specified range 

      Refer to DTC P0106 

    • If within the specified range 
  3. Engine running at the operating temperature.
  4. Verify the Long Term Fuel Trim parameter is between -21% and +38.5%.
    • If greater than +38.5% 
    1. Ignition OFF.
    2. Inspect for the conditions listed below:
      • Mass air flow (MAF) sensor signal skewed. If the Short Term Fuel Trim parameter changes greater than 20% when the MAF sensor is disconnected, refer to DTC P0101 .
      • Fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
      • Missing, restricted, or leaking exhaust components. Refer to Symptoms - Engine Exhaust .
      • Malfunctioning fuel injectors. Refer to Fuel Injector Diagnosis .
      • Split, kinked or improperly connected vacuum hoses.
      • Insufficient fuel in the tank
      • Low fuel pressure. Refer to Fuel System Diagnosis .
      • Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings.
      • Leaks in the air induction system and the air intake ducts
      • Missing air filter element
      • Cracked EVAP canister
      • Evaporative pipes obstructed or leaking
      • Leaks in the crankcase ventilation system. Refer to Crankcase Ventilation System Inspection/Diagnosis .
        • If a condition is found, repair as necessary.
        • If no condition is found, inspect the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .
    • If less than -21% 
    1. Ignition OFF.
    2. Inspect for the conditions listed below:
      • Mass air flow (MAF) sensor signal skewed. If the Short Term Fuel Trim parameters for both banks changes greater than 20% when the MAF sensor is disconnected, refer to DTC P0101 .
      • Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
      • Missing, restricted, or leaking exhaust components-Refer to Symptoms - Engine Exhaust .
      • Malfunctioning fuel injectors-Refer to Fuel Injector Diagnosis
      • Collapsed or restricted air intake duct
      • Excessive fuel pressure - Refer to Fuel System Diagnosis
      • Dirty or restricted air filter
      • Objects blocking the throttle body
      • Improper operation of the evaporative emissions control system
      • Excessive fuel in the crankcase. Change the engine oil as necessary.
    • If a condition is found, repair as necessary.
    • If no condition is found, inspect the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .
    • If between -21% and +38.5% 
  5. All OK.
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